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js-codemod

This repository contains a collection of codemod scripts for use with JSCodeshift.

Setup & Run

npm install -g jscodeshift
git clone https://github.com/cpojer/js-codemod.git
jscodeshift -t <codemod-script> <file>

Use the -d option for a dry-run and use -p to print the output for comparison.

Included Scripts

arrow-function-arguments

jscodeshift -t js-codemod/transforms/arrow-function-arguments.js <file>

arrow-function

Transforms callbacks only when it can guarantee it won't break this context in the function. Also transforms function() { }.bind(this) calls to () => {}.

jscodeshift -t js-codemod/transforms/arrow-function.js <file>

Options:

--inline-single-expressions=true: If you are feeling lucky and you know that returning the value of single-expression functions will not affect the behavior of your application you can specify the option and it will transform function() { relay(); } to () => relay() instead of () => { relay(); }.

--max-width=120: Try the best it can to keep line lengths under the specified length.

invalid-requires

jscodeshift -t js-codemod/transforms/invalid-requires.js <file>

jest-update

jscodeshift -t js-codemod/transforms/jest-update.js <file>

no-reassign-params

Converts functions to not reassign to parameters. This is useful to turn on in conjunction with Flow's const_params option.

jscodeshift -t js-codemod/transforms/no-reassign-params.js <file>

no-vars

Conservatively converts var to const or let.

jscodeshift -t js-codemod/transforms/no-vars.js <file>

object-shorthand

Transforms object literals to use ES6 shorthand for properties and methods.

jscodeshift -t js-codemod/transforms/object-shorthand.js <file>

outline-require

jscodeshift -t js-codemod/transforms/outline-require.js <file>

rm-copyProperties

jscodeshift -t js-codemod/transforms/rm-copyProperties.js <file>

rm-merge

jscodeshift -t js-codemod/transforms/rm-merge.js <file>

rm-object-assign

jscodeshift -t js-codemod/transforms/rm-object-assign.js <file>

rm-requires

Removes any requires where the imported value is not referenced. Additionally if any module is required more than once the two requires will be merged.

jscodeshift -t js-codemod/transforms/rm-requires.js <file>

template-literals

Replaces string concatenation with template literals.

jscodeshift -t js-codemod/transforms/template-literals.js <file>

Adapted from "How to write a codemod" by Ramana Venkata.

Areas of improvement:

• Comments in the middle of string concatenation are currently added before the string but after the assignment. Perhaps in these situations, the string concatenation should be preserved as-is.

• Nested concatenation inside template literals is not currently simplified. Currently, a + b${'c' + d} becomes ${a}b${'c' + d} but it would ideally become ${a}b${`c${d}`}.

• Unnecessary escaping of quotes from the resulting template literals is currently not removed. This is possibly the domain of a different transform.

• Unicode escape sequences are converted to unicode characters when the simplified concatenation results in a string literal instead of a template literal. It would be nice to perserve the original--whether it be a unicode escape sequence or a unicode character.

touchable

jscodeshift -t js-codemod/transforms/touchable.js <file>

trailing-commas

Adds trailing commas to array and object literals.

jscodeshift -t js-codemod/transforms/trailing-commas.js <file>

unchain-variables

Unchains chained variable declarations.

jscodeshift -t js-codemod/transforms/unchain-variables.js <file>

underscore-to-lodash-native

Replaces underscore (or lodash) to ES6 + lodash, preferring native ES6 array methods. Member imports are used by default to allow tree-shaking, but the --split-imports=true option will split each lodash import into its own lodash/<method> import.

jscodeshift -t js-codemod/transforms/underscore-to-lodash-native.js <file>

unquote-properties

Removes quotes from object properties whose keys are strings which are valid identifiers.

jscodeshift -t js-codemod/transforms/unquote-properties.js <file>

updated-computed-props

jscodeshift -t js-codemod/transforms/updated-computed-props.js <file>

use-strict

Adds a top-level 'use strict' statement to JavaScript files

jscodeshift -t js-codemod/transforms/use-strict.js <file>

Included extensions

jscodeshift-imports helpers for modifying import and require statements, see docs.

Recast Options

Options to recast's printer can be provided through the printOptions command line argument

jscodeshift -t transform.js <file> --printOptions='{"quote":"double"}'